MSK - Biochemistry - Actin & Intermediate Filaments; Collagen; ECM Flashcards by Jason Worley

What is the inheritance pattern of Duchenne’s muscular dystrophy?

What is the life expectancy of affected individuals?

X-linked recessive;

< 35

How well did you know this?

Not at all

Perfectly

Duchenne’s muscular dystrophy affects which muscles first?

What muscles often appear hypertrophied?

What is the usual cause of death?

The pelvic girdle;

calf muscles;

loss of function of diaphragmatic and cardiac muscle

How well did you know this?

Not at all

Perfectly

What type of muscle is the principal type affected in Duchenne’s muscular dystrophy?

What is a common first sign?

Voluntary;

failure of child to walk normally or hold normal posture - may walk on toes due to muscle contractures

How well did you know this?

Not at all

Perfectly

Dystrophin binds actin to ____________, which binds to extracellular laminin.

α,β-dystroglycan

How well did you know this?

Not at all

Perfectly

What disease is similar to Duchenne’s muscular dystrophy but is less severe and results later in life?

Becker muscular dystrophy

How well did you know this?

Not at all

Perfectly

What two substances (one mineral and one nucleotide) are vital to F-actin polymerization from G-actin?

ATP, Mg²⁺

How well did you know this?

Not at all

Perfectly

The ATP-binding cleft is on which end of the G-actin monomer?

The - end

How well did you know this?

Not at all

Perfectly

G-actin must be bound to ___ to polymerize into F-actin.

α- and β-tubulin must be bound to ___ to polymerize into microtubule protofilaments.

ATP;

GTP

How well did you know this?

Not at all

Perfectly

True/False.

Both the GTP associated with microtubules and the ATP associated with actin will hydrolyze relatively soon after polymerization?

True

(although the ATP-actin hydrolyzes much sooner)

How well did you know this?

Not at all

Perfectly

What are the three cellular proteins regulating actin polymerization?

Cofilin,

profilin,

thymosin-β₄

How well did you know this?

Not at all

Perfectly

What protein breaks off pieces of F-actin?

Cofilin

How well did you know this?

Not at all

Perfectly

What protein exchanges ADP for ATP on G-actin, allowing it to be used in polymerization?

(It just adds a phosphate group to the ADP)

Profilin

How well did you know this?

Not at all

Perfectly

What protein sequesters ATP G-actin to prevent polymerization?

Thymosin-β₄

How well did you know this?

Not at all

Perfectly

What protein binds the + end of F-actin to prevent polymerization?

What protein binds the - end of F-actin to stabilize actin?

CapZ;

tropomodulin

How well did you know this?

Not at all

Perfectly

What protein binds the + end of F-actin to prevent polymerization?

CapZ

How well did you know this?

Not at all

Perfectly

What protein binds the - end of F-actin to stabilize actin?

Tropomodulin

How well did you know this?

Not at all

Perfectly

What protein helps promote the unbranched form of F-actin?

What protein helps promote the branched form of F-actin?

Formin;

Arp2/3

How well did you know this?

Not at all

Perfectly

What type of filament is especially important in cell migration (e.g. chemotaxis)?

Actin (microfilaments)

How well did you know this?

Not at all

Perfectly

What are the four steps of cell movement during chemotaxis?

1. Foot process (lamellipodium) formation

2. Adhesion at the front of the cell

3. Translocation as the cell shifts forwards

4. Deadhesion at the back of the cell

How well did you know this?

Not at all

Perfectly

What type of protein cross-links the cytoskeleton to the ECM?

Integrins

How well did you know this?

Not at all

Perfectly

What type of protein cross-links actin into a meshwork on the P-face?

Spectrin

How well did you know this?

Not at all

Perfectly

Hereditary spherocytosis can be caused by defects in what three proteins?

Spectrin, protein 4.1, ankyrin.

How well did you know this?

Not at all

Perfectly

What type(s) of intermediate filament are especially prevalent in epithelial tissues?

Cytokeratins (acidic and basic)

How well did you know this?

Not at all

Perfectly

What type(s) of intermediate filament are especially prevalent in muscle?

Desmin

How well did you know this?

Not at all

Perfectly

What type(s) of intermediate filament are especially prevalent in mesenchymal tissues?

Vimentin

What type(s) of intermediate filament are especially prevalent in glial cells?

GFAP

What type(s) of intermediate filament are especially prevalent in neural tissues?

Neurofilaments

What type(s) of intermediate filament is especially prevalent in the nucleus?

Lamins

What protein other than spectrin or dytrophin is especially important in cross-linking actin into its structure on the inner cell membrane?

Fimbrin

What protein is especially important in organizing actin stress fibers during cell migration?

α-actinin

Spectrin and dystrophin are both in what supergene family?

Spectrin

What are some of the physical features commonly seen in type I osteogenesis imperfecta? What are some other common occurrences?

Blue sclera, triangular shape; frequent fractures, hearing loss (beginning in the twenties), scoliosis, thin skin, loose joints, low muscle tone, brittle teeth

What inheritance does type I osteogenesis imperfecta exhibit? It is due to a defect in what?

Autosomal dominant; type I collagen

What type of osteogenesis imperfecta frequently results in death during embryogenesis or birth?

Type II

What gene is associated with osteogenesis imperfecta type I?

*COL1A1*

How is osteogenesis imperfecta treated? What is the mechanism of action?

Bisphosphonates; osteoclast inhibition

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ are useful for treating osteoporosis and osteogenesis imperfecta by inhibiting osteoclasts because they mimic \_\_\_\_\_\_\_\_\_\_\_\_\_\_, which is needed for normal osteoclastic activity.

Bisphosphonates; pyrophosphates

How do individuals with type II osteogenesis imperfecta typically die?

Severe bone fracturing during the birthing process

What effect do bisphosphonates tend to have on apoptosis in bone cells?

Increased osteoclast apoptosis; decreased osteoblast apoptosis

The basic structure of collagen that gives it its strength is a:

triple helix

What is the basic repeating amino acid code for collagen? What amino acids make up the variable portions?

Gly - X - Y; X,Y = proline or hydroxyproline

Is the collagen helix a right- or left-handed helix?

Left

What type of bonding is extremely prevalent in collagen, binding the strands together?

Hydrogen bonding

Describe collagen in terms of tensile strength and elasticity. Describe elastin in terms of tensile strength and elasticity.

High tensile strength, low elasticity; low tensile strength, high elasticity;

Vitamin C is needed for what step of collagen formation? Why is this step important?

Proline hydroxylation; it stabilizes the triple helix

**True/False.** Without Vitamin C, collagen cannot be synthesized.

**False.** Vitamin C is responsible for post-translational proline hydroxylation. *(without vitamin C, the collagen strands are simply less stable and more easily degraded)*

Vitamin C is a cofactor of what enzyme involved in post-translational collagen modification?

4-prolyl-hydroxylase

Which five collagen fibrils follow the characteristic triple helix structure?

I, II, III, V, XI

What type of collagen is a higher order structure found in the basement membrane?

Type IV

What type of collagen is an anchoring type that connects the dermal and epidermal layers?

Type VII

What organ systems are most susceptible in Alport's syndrome? What is the main genetic defect in Alport's syndrome?

Kidney, ears (ossicles), and eyes (cornea); type IV collagen defects

What is the most common form of inheritance seen in Alport;s syndrome?

X-linked

Where is type I collagen found?

Most connective tissue

Where is type II collagen found?

Cartilage and vitreous humor

Where is type III collagen found?

Extensible connective tissue

Where is type IV collagen found? What structure does it have?

Basal lamina; sheet-like networks

Where are type V and XII collagen found?

Tissues containing type I collagen

Where is type VII collagen found?

Anchoring basal lamina to underlying connective tissue

What protein serves as a scaffold for tropoelastin? Mutations in this protein lead to what disorder?

Fibrillin; Marfan's syndrome

What is a (typically present) symptom of homocystinuria that differentiates it from Marfan's syndrome?

Intellectual disability

What are the first three steps of collagen synthesis? (starting with a transcribed collagen mRNA)

**1.** mRNA is translated into pre-procollagen **2.** Hydroxylation of select proline residues **3.** Glycosylation of select lysine residues

What are the second three steps of collagen synthesis? (starting here with hydroxylated and glycosylated procollagen chains)

4. Three pro-alpha-chains come together into an alpha-helix 5. Procollagen secreted from cell 6. Procollagen ends cleaved off by procollagen peptidase (This is now **tropocollagen**)

Following secretion of procollagen from the cell and cleavage of its ends to form tropocollagen, what happens?

Lysyl oxidase cross-links mature collagen fibrils

A deficiency of lysyl oxidase leads to what disorder? Lysyl oxidase is used to cross-link what together? What element is necessary for its function?

Menke's syndrome; collagen fibrils; copper

Ehrlos-Danlos syndrome is caused by a mutation in the *ADAMTS2* gene. This leads to a deficiency in what enzyme? What does this enzyme do?

Procollagen peptidase; cleaves procollagen ends to form tropocollagen

What are three of the few enzymes in the body that require copper (Cu²⁺) as a cofactor?

Tyrosinase, dopamine β-hydroxylase, lysyl oxidase

How does the ECM serve as a source of growth and chemotactic factors?

Growth factors are bound to (sequestered in) **proteoglycans** until metalloproteases release them

What is the basic makeup of ECM? | (3 main players)

Hydrated gel + reinforcing fibers throughout + multiadhesive signaling proteins

What proteoglycan is associated with the basement membrane? What collagen type is associated with the basement membrane? What multiadhesive proteins are associated with the basement membrane?

Perlecan; type IV; fibronectin, laminin

What proteoglycan is associated with the basement membrane?

Perlecan

What collagen type is associated with the basement membrane?

Type IV

What multiadhesive proteins are associated with the basement membrane?

Fibronectin, laminin

What are the two main functions of multiadhesive proteins in the ECM?

Signaling, binding cells in place within the ECM

What is a glycosaminoglycan (GAG) in terms of structure? Are they osmotically active?

An unbranched polysaccharide made of repeating disaccharide units (often a uronic acid + an amino sugar); yes, they keep tissues hydrated by storing water

Are glycosaminoglycans eosinophilic or basophilic? Why?

Basophilic; lots of SO₄^- and COO^- groups

What is a proteoglycan (found in the ECM)?

A core protein with tons of attached glycosaminoglycans (basically a protein with tons of sugars sticking off of it) *(one branch of the 'Christmas tree' seen in the attached illustration)*

What is the major core protein of proteoglycans found on articular cartilage? **True/false.** It can absorb and release synovial fluid as needed (according to pressures).

Aggrecan; true

What are the two main cartilaginous proteins that are often degraded in osteoarthritis?

Type II collagen; aggrecan

Is hyaluronic acid a proteoglycan?

No; it is a glycosaminoglycan forming the 'trunk' to which proteoglycan 'branches' attach

What type of proteoglycan is primarily found in cartilage? What type of proteoglycan is primarily found in basal lamina? What type of proteoglycan binds type I collagen and is widespread in ECM?

Aggrecan; perlecan; decorin

What two proteoglycans and one protein sequester TGF-β?

**Aggrecan, decorin** (storing it until the tissue is damaged and growth is needed); **fibrillin** (that's why Marfan's syndrome patients have such long bones)

Why do individuals with Marfan's syndrome grow such long bones?

**Fibrillin** (which is missing or defective in these patients) **sequesters TGF-β**

What is a super-abundant protein of the ECM that binds type I collagen, fibrin, and proteoglycans to integrins on cell membranes, essentially binding cells to ECM?

Fibronectin

What is fibronectin's main function?

Connecting cells to ECM

Multiadhesive proteins are ECM proteins such as fibronectin and laminin. What is another protein in this family that is essential to proper blood coagulation?

von Willebrand's factor

What is the principal multiadhesive protein of the basal lamina? What cell membrane protein does it bind? What particular basal lamina protein does it bind?

Laminin-1; α,β-dystroglycan; type IV collagen

What are the two main families of protein involved in cell-to-cell adhesion?

**Cadherins** (found in desmosomes); **CAMs** (cell adhesion molecules)

Inflammatory molecules induce endothelial cells to express what protein that loosely interacts with leukocytes? After that initial velcro-like contact, what stronger protein binds the leukocyte and helps is extravasate?

P-selectins; integrins

Describe integrin structure. **True/False.** Integrins are present in both active and inactive forms.

Heterodimeric (α and β) **True.**

The inactive conformation of an integrin protein is: The active conformation of an integrin protein is:

Bent; extended

What are a few intracellular pathways that may be involved in different integrin protein signaling?

ERK 1/2 The Phosphatidyl Inositol 3- Kinase (PI3K) pathway Rac / Rho / Cdc42 G-proteins

The _ \_ _ sequence is important to integrin signaling.

RGD

What multiadhesive protein is often found in the basal lamina along with perlecan?

Agrin

Are collagen chains stabilized by *inter*chain or *intra*chain hydrogen bonds?

Interchain | (there are no intrachain H-bonds)